Apparatus for controlling a hydraulic-lift tail gate arrangement of a cargo-carrying vehicle

ABSTRACT

The apparatus comprises a double-acting consumer having a first work conduit for receipt of pressure fluid to cause the consumer to effect movement of a load in a first direction and having a second work conduit for receipt of pressure fluid to cause the consumer to effect movement of the load in opposite second direction. The apparatus includes a tank, a supply conduit and a pump for pumping fluid from the tank into the supply conduit, a second port connected to the tank, a third port, and a fourth port connected to the second work conduit of the double-acting consumer. The selector valve has a first position in which fluid communication is established in the selector valve between the first and fourth ports and also between the second and third ports. The selector valve has a second position in which fluid communication is established in the selector valve between the first and third ports and also between the second and fourth ports. A control valve has a first port connected to the first work conduit of the double-acting consumer and has a second port connected to the third port of the selector valve. The control valve has a first position in which fluid communication between the ports of the control valve in the control valve is blocked. The control valve has a second position in which fluid communication between the ports of the control valve in the control valve is established. A pressure-regulating device is connected between the fourth port of the selector valve and the tank and is operative for regulating the pressure of fluid in the second work conduit of the double-acting consumer.

United States Patent [1 1 Herrmann Dec. 3, 1974 APPARATUS FOR CONTROLLING A HYDRAULIC-LIFT TAIL GATE ARRANGEMENT OF A CARGO-CARRYING VEHICLE [75] Inventor: Walter Herrmann, Vaihingen/Enz,

Germany [73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany 22 Filed: Dec. 12, 1973 211 App]. No.: 422,595

[30] Foreign Application Priority Data Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or FirmMichael S. Striker [57] ABSTRACT The apparatus comprises a double-acting consumer.

VALVE 24 m (SEATED VALVE MEMBER .TYPE) having a first work conduit for receipt of pressure fluid to cause the consumer to effect movement of a load in a first direction and having a second work conduit for receipt of pressure fluid to cause the consumer to effect movement of the load in opposite second direction. The apparatus includes a tank, a supply conduit and a pump for pumping fluid from the tank into the supply conduit, a second port connected to the tank, a third port, and a fourth port connected to the second work conduit of the double-acting consumer. The selector valve has a first position in which fluid communication is established in the selector valve between the first and fourth ports and also between the second and third ports. The selector valve has a second position in which fluid communication is established in the selector valve between the first and third ports and also between the second and fourth ports. A control valve has a first port connected to the first work conduit of the double-acting consumer and has a second port connected to the third port of the selector valve. The control valve has a first position in which fluid communication between the ports of the control valve in the control valve is blocked. The control valve has a second position in which fluid communication between the ports of the control valve in the control valve is established. A pressure-regulating device is connected between the fourth port of the selector valve and the tank and is operative for regulating the pressure of fluid in the second work conduit of the double-acting consumer.

18 Claims, 3 Drawing Figures VALVE SEATED VALVE MEMBER. TYPE) Fig.1

PATENTE; 553 3 4 APPARATUS FOR CONTROLLING A HYDRAULIC-LIFT TAIL GATE ARRANGEMENT OF A CARGO-CARRYING VEHICLE BACKGROUND OF THE INVENTION The invention relates to a hydraulic control arrangement for one or more, particularly two or more, consumers, each of which is provided with a respective control valve operative for establishing or terminating communication between a work conduit of the consumer and a main conduit serving for the conveyance of fluid into and alternatively out from such work conduit of the consumer. More particularly, the type of control arrangement in question further includes a selector valve connected to all of the control valves and operative for connecting the just-mentioned main conduit either to a source of pressure fluid or else to a tank. With this kind of arrangement, a particular control valve is actuated if it is desired to activate a respective one of the consumers, and the selector valve is activated in a manner determining the direction of flow of fluid through the work conduit of the consumer, for example so as to move the piston of a cylinder-and-piston unit in one or the other direction relative to the cylinder thereof.

Arrangements of the type just described are already known in which highly seal-tight control valves of the seated-valve-member type are used to each control a single-acting consumer, with a selector valve being connected to all of the control valves to determine whether fluid should flow into or out of the selected single-acting consumer. If double-acting consumers are to be controlled; it is necessary according to the con- SUMMARY OF THE INVENTlON It is the general object of the present invention to provide a control arrngement for one or more hydraulic consumers, and especially for two or more hydraulic consumers, which makes use'of a valve arrangement of the type conventionally employed for the control of single-acting consumers, but which through a few simple modificatins and additions can be adapted for the control of double-acting consumers.

This object, and others which will become more understandable from the following description of preferred embodiments, can be met according to one advantageous concept of the invention by providing a hydraulic control apparatus comprising a double-acting consumer having a first work conduit for receipt of pressure fluid to cause the consumer to effect movement of a load in a first direction and having a second work conduit for receipt of pressure fluid to cause the consumer to effect movement of the load in opposite second direction. The apparatus includes a tank, a supply conduit and a pump for pumping fluid from the tank into the supply conduit. A selector valve has a first port connected to the supply conduit, a second port connected to the tank, a third port, and a fourth port connected to the second work conduit of the doubleacting consumer. The selector valve has a first position in which fluid communication is established in the selector valve between the first and fourth ports and also between the second and third ports. The selector valve has a second position in which fluid communication is established in the selector valve between the first and third ports and also between the second and fourth ports. A control valve has a first port connected to the first work conduit of the double-acting consumer and has a second port connected to the third port of the selector valve. The control valve has a first position in which fluid communication between the ports of the control valve in the control valve is blocked. The control valve has a second position in which fluid communication between the ports of the control valve in the control valve is established. Pressure-regulating means is connected between the fourth port of the selector valve and the tank and is operative for regulating the fluid pressure in the second work conduit of the double-acting consumer.

With the inventive valve arrangement, it is possible to employ mass-produced valve elements for the control of double-acting consumers in a highly seal-tight manner.

It is particularly simple and advantageous according to the invention to control the operation of two doubleacting consumers, by connecting the second work conduit of each double-acting consumer to the fourth port of the selector valve.

It is also advantageous to provide between the first and second ports of the selector valve a check valve oriented to permit fluid flow from the second port to the first port of the selector valve. This makes possible a sucking up of fluid into the second work conduit of the double-acting consumer in certain situations explained in detail below. In particular, this sucking up of fluid into the double-acting consumer would for example occur if the double-acting consumer is a cylinderand-piston unit the piston of which is being moved not hydraulically but solely under the action of the weight of the supported load. Fluid would be sucked up into the chamber of increasing volume, thereby preventing the development of underpressure in such chamber.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRlPTlON OF THE DRAWING FIG. 1 depicts a first embodiment of the invention;

FIG. 2 depicts a portion of a second embodiment of the invention; and

FIG. 3 depicts a portion of a third embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 depicts a control arrangement 11 for the conto a horizontal orientation at a level flush with the floor of the cargo compartment of the van, so that cargo can be rolled or slid onto the tail gate. Thereafter, the horizontally oriented tail gate is lowered in vertical direction to the street level, for example, so that the cargo can be rolled or slid off the tail gate and onto the street.

New cargo may be rolled or slid onto the tail gate from the street, and the horizontally oriented tail gate will be raised vertically back to a level flush with the cargo compartment floor, so that the new cargo can be rolled or 'slid into the cargo compartment. Finally, the tail gate will be swung upwardly back to its initial vertically oriented closed position. Alternatively, the downward swinging and vertical lowering of the tail gate can occur simultaneously, and/or the upward swinging and vertical raising of the tail gate can occur simultaneously.

The swinging movement of the tail gate is effected by the cylinder-and-piston unit 12, and the purely vertical movement of the tail gate is effected by the cylinderand-piston unit 13. When the tail gate is in upwardly swung position the piston of unit 12 is in the upper position thereof; when the tail gate is in downwardly swung position the piston of unit 12 is in the lower position thereof. When the tail gate is in vertically elevated position the piston of unit 13 is in the upper position, when the tail gate is in vertically lowered position the piston of unit 13 is in the lower position thereof.

The control arrangement 11 for the control of the units 12, 13 is comprised ofa connecting unit 14, an intermediate unit 16 incorporating a preselector valve 15, and a valve unit 19 incorporating two control valves 17 and 18.

The control valves 17 and 18 are identical to each other, in the illustrated embodiment, and are of the seated-valve-member type. Valves of the seated-valvemember type have one or more movable valve members which when blocking the flow through a valve port abut against a valve seat with an abutment force having a component oriented in the direction of flow through such port. This is in contrast to valves of the slidingspool type wherein blocking off of a port does not involve such abutment of a valve member against a valve seat. Valves of the seated-valve'member type are characterized by a seal-tightness inherently. superior to that of valves of the sliding-spool type.

The two valves l7, 18 each include a schematically I depicted valve member 21 normally maintained by'a respective biasing spring 22 in a first position 23 blocking communication between the first work conduits 25 of the consumers l2, 13, on the one hand, and the conduit 24, on the other hand. The conduit 24 serves alternately as a supply conduit for pressure fluid and as a return conduit leading to a tank 36.

Each valve 17, 18 is provided with a respective single-acting electromagnet 26 which, when energized, opposes the biasing force of the respective spring 22 and moves the respective valve member 21 to the second position 27 thereof, in which bidirectional communication is established between the conduit 24 and the first work conduits 25 of the two consumers 12, 13. The respective first work conduits 25 of the cylinderand-piston units 12, 13 convey fluid into and out of the respective lower chambers 28, 29 of the units 12, 13.

The preselector valve in the intermediate unit 16 has a first port 31 connected with a pressure fluid supply conduit 32 in the connecting unit 14. Pressure fluid supply conduit 32 conveys fluid pumped from tank 36 by a pump 33, which is driven by an electromotor 30.

The preselector valve 15 has a second port 34 which discharges into tank 36 via return conduit 35. The valve 15 has a third port 37 connected to the conduit 24 of valve unit 19, and has a fourth port 38 connected to a second conduit 39. Second conduit 39 is connected to conduit 41, which branches off into two second work conduits of the double-acting consumers 12, 13. These second work conduits convey fluid into and out of the respective upper chambers 42, 43 of the consumers 12, 13.

The connection unit 14 incorporates a pressurelimiting valve 49 which limits the pressure in supply conduit 32, and a check valve 51 which is oriented to permit flow of fluid into the first port 31 of valve 15. A further check valve 52 is connected between the supply conduit 32 and the return conduit 35 withsuch an orientation as to permit a sucking up of fluid out of return conduit 35 and into port 31 of valve 15 in a manner described below. The connection unit 14 furthermore incorporates an adjustable flow restrictor 53 located in a third conduit 54 connected between the second conduit 39 and the return conduit 35. The conduit 24 of the valve unit 19 is closed at its end by a suitable plug 55.

The arrangement of FIG. 1 operates as follows:

It is initially assumed that the hydraulic-lift tail gate is in the upwardly swung and vertically elevated position, with the pistons of cylinder-and-piston units 12, 13 accordingly being in their illustrated upper positions. The valve members 21 of the control valves l7, 18 are in the position 23 thereof, and the valve member 44 of the preselector valve 15 is in the position 46 thereof. The load acting on the pistons of units 12 and 13 exerts a downward force upon the pistons. The cylinder chambers 28, 29 are tightly sealed by the valves 17, 18 of the seated-valve-member type, and accordingly the pistons of the units 12, 13 are hydraulically blocked. I

To cause the tail gate to swing downwards to a horizontal orientation, the following is done: The van driver presses a non-illustrated button to effect energization of the solenoid 26 of control valve 17, and the valve member 21 of valve 17 accordingly assumes the second position 27 thereof. The pump 33 is not caused to operate at this time. The tail gate swings downwardly under its own weight, expelling hydraulic fluid from cylinder chamber 28, the fluid flowing out through the respective conduit 25, through the valve 17, through the first conduit 24, through the non-activated preselector valve 15, through the return conduit 35, and into tank 36. Simultaneously, the descending piston of unit 12 sucks fluid up into cylinder chamber 42, via the check valve 52, the valve 15, the second conduit 39 and the conduit 41. Also, fluid will be sucked up into the chamber 42 to some extent via the third conduit 54 containing the flow restrictor 53.

If the van is parked on a downward incline, it may happen that the end gates own weight will tend to maintain it in upwardly swung position, in which case the piston of hydraulic unit 12 will not descend even with control valve 17 in the second position 27 thereof. If this occurs, the van driver pushes another nonillustrated button to energize the electromotor 30. As a result, the pump 33 pumps pressure fluid through the supply conduit 32, through the preselector valve 15, through the second conduit 39 and the conduit 41, into the cylinder chamber 42. Simultaneously therewith, a portion of the fluid flowing through conduit 39 does not reach conduit 41, and is instead diverted back to tank 36 via third conduit 54. The fluid flow in conduit 41 is not short-circuited by provision of conduit 54, because of the provision of the flow restrictor 53 in conduit 54. The purpose of providing the conduit 54 with the flow restrictor 53 is to effect, in a very simple manner, an automatic reduction in the pressure of the work fluid when the work fluid is employed to drive one or both of the pistons of units 12, 13 in downward direction. This reduced work pressure will be substantially lower than the prssure established by the pressure limiting valve 49 for the work fluid pumped into the lower cylinder chambers 28, 29. This is appropriate, because the pressure necessary to effect downward swinging or vertical lowering of the tail gate when the tail gates own weight is incapable of satisfactorily effecting such movement, is evidently considerably lower than the pressure necessary to effect vertical raising or upward swinging of the tail gate. The two work pressures, i.e., the work pressure established by valve 49 for piston lifting and the pressure established by restrictor 53 for piston lowering, may differ by a ratio of 7:1.

When it is desired to effect upward swinging of the tail gate to its vertical or closed orientation, the following is done: The van driver presses a non-illustrated button which simultaneously energizes the solenoids 26 and 47 of the valves 17 and 15 and also drive motor 30 of pump 33. The valve 17 accordingly assumes its second position 27, and the valve 15 assumes its second position 48. The pump 33 pumps pressure fluid through supply conduit 32, through preselector valve 15, throough the conduit 24 and the control valve 17 and into the lower cylinder chamber 28 of the unit 12. The pressure established in this fluid flow path is maintained at a predetermined value by the pressure-limiting valve 49. Simultaneously therewith, pressure fluid is expelled by the rising piston of unit 12 out of the chamber 42 and through the conduit 41, the second conduit 39, the

selector valve 15 and into the return conduit 35. The

liquid expelled from chamber 42 and travelling through line 41 is partially diverted along another path through conduit 54, also leading into the return conduit 35. The diversion of fluid flow into conduit 54 is evidently only partial, because of the provision therein of the flow restrictor 53.

The combination of the preselector valve 15 and the control valve 17, which per se are conventionally employed only for the control of a single-acting consumer, can accordingly be used together to control a doubleacting consumer.

The control of the position of the piston of cylinderand-piston unit 13 is exactly analogous to the control of the position of the piston of the unit 12, just described. However, as mentioned before, the unit 13 controls the upward and downward vertical movement of the tail gate, whereas the unit 12 controls the upward and downward swinging movement thereof. By pressing a non-illustrated button, the solenoid 26 of valve 16 is energized, and the piston of unit 13 will descend under the weight of the tail gate and any supported cargo. Alternatively, tail gate descent can be effected by pressing a different non-illustrated button which entromotor 30, so that pressure fluid will be pumped into chamber 43 to push the associated piston down by hydraulic force. To raise the tail gate, a non-illustrated button is pressed to energize the solenoids 26 and 47 of the valves 18 and 15 and to simultaneously energize the pump motor 30.

As a still further possibility, the cylinder chambers 28, 29 can be supplied with pressure fluid simultaneously, to effect simultaneously an upward swinging and a vertical raising of the tail gate. Likewise, the chambers 28, 29 can be discharged simultaneously, to effect a simultaneous downward swinging and vertical lowering of the tail gate.

FIG. 2 depicts a structure 60 composed of two units 61, 62 which could respectively replace the units 14 and 16 of FIG. 1, to form a second embodiment of the inventive control apparatus. Components in unit 60 of FIG. 2 identical to components in units l4, 16 of FIG. 1 are denoted by the same reference numerals.

The unit 61 of FIG. 2 differs from unit 14 of FIG. 1 in the following respects:: The pressure-reducing conduit 54 with flow restrictor 53 therein employed in F IG. 1 is replaced by a pressure-limiting valve 63. Also,- the check valve 52 of FIG. 1 is omitted in FIG. 2.

. The unit 62 of FIG. 2 differs from unit 16 of FIG. 1 in the following respects: The four-port two-position preselector valve 15 of FIG. 1 is replaced in FIG. 2 by a four-port three-position preselector valve 64. The first and second positions 46, 48 of valve 64 are identical to those of valve 15. However, the schematically depicted valve member 65 of valve 64 is movable to an intermediate third position 66 in which it blocks the first port 31 and connects together the three remaining ports 37, 38 and 34. Also, the three-position valve 64 is provided with two electromagnets 67, each of which when energized brings the valve into a respective one 7 of the end positions thereof. The intermediate position ergizes both the solenoid 26, of valve 17 and the eleci 66 is maintained by biasing springs when both electromagnets 67 are unenergized.

The differences in operation of the FIG. 1 and FIG. 2 embodiments are as follows:

In the FIG. 2 embodiment, when the pistons of units l2, 13 are lowered solely under the weight of the tail gate, pressure fluid will be sucked into the cylinder chambers 42, 43 directly from the return conduit 35, the valve 64 being in the intermediate position 66 thereof in such situation. If the pistons of units 12, 13 are to be lowered by pumping hydraulic fluid into the upper chambers 42, 43 thereof, the valve 64 is brought to its first position 46. Accordingly, as such pumping occurs, the pressure reaching the upper cylinders'42 and/or 43 will be the pressure established by pressurelimiting valve 63. Such pressure can be maintained by the pressure-limiting valve 63 at a relatively exact value, in contrast to the use in FIG. 1 of the restricted conduit 54 which brings with it viscosityand flow-ratedependent pressure oscillations, to some extent.

FIG. 3 depicts a structure 70 composed of two units 71, 72 which cn be substituted for the units 14, 16 of FIG. 1, to form a third embodiment of the inventive control apparatus. Components in units 71, 72 of FIG. 3 identical to components in units 61, 62 of FIG. 2 are denoted by the same reference numerals.

In FIG. 3, the unit 71 again includes a check valve 52 through which fluid can be sucked out of the return conduit 35 and into the upper cylinder chambers 42, 43 when the pistons of units 12, 13 are lowered solely under the weight of the tail gate. The unit 72 contains a three-position valve 74 similar to valve 64 of FIG. 2. However, in the intermediate position 75 of valve 74 all four ports 31, 34, 37, 38 are blocked.

The F IG. 3 embodiment operates differently from the FIG. 2 embodiment in the following respects:

When the preselector valve 74 is in the intermediate position 75, the pistons of units 12, 13 are hydraulically blocked with respect to the possibility of downward movement, and are in effect hydraulically blocked with respect to the possibility of upward movement, by reason of the provision of the pressure-limiting valve 63 in the conduit 54. To effect downward swinging and/or vertical lowering of the tail gate, either under the weight of the tail gate alone or else by actually pumping pressure fluid into the chambers 42 and/or 43, the preselector valve 74 of FIG. 3 is moved to first position 46, as with the preselector valve 15 of FIG. 1. The work pressure to effect hydraulic lowering of the pistons of units l2, 13 is established by the pressurelimiting valve 63, instead of by the flow restrictor 53 of FIG. 1. When the pistons of units 12, 13 are to be hydraulically lifted, to either upwardly swing or vertically elevate the tail gate, all of the fluid expelled from the upper cylinder chambers 42 and/or 43 flows to the return conduit 35 via the preselector valve 74, since there is no additional parallel-connected path through a flow restrictor. The pressure developed in the upper cylinder chambers 42, 43 in such situation is lower than the pressure which causes pressure-limiting valve 63 to open.

Modifications of the illustrated structure are possible within the scope of the inventive concept. For example, in FIG. 1 the check valve 52 can be omitted altogether, if the flow restrictor 53 is so dimensioned as to be able to carry all the fluid to be sucked into upper cylinder chambers 42, 43 when the pistons of units 12, 13 are lowered not hydraulically but solely under the weight of the tail gate. As another possibility, the control arrangement can be used to control the operation of one single-acting and one double-acting consumer, instead of two double-acting consumers as in the illustrated embodiments.

It will be understood that each of the elements described'above, or two or more together, may also find a useful application in other types of hydraulic circuits and constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a hydraulic control apparatus for controlling the operation of a hydraulic-lift tail gate of a moving van, or the like, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims: 1. A hydraulic control apparatus comprising, in combination, a double-acting consumer having a first work conduit for receipt of pressure fluid to cause said consumer to effect movement of a load in a first direction and having a second work conduit for receipt of pressure fluid to cause said consumer to effect movement of such load in opposite second direction; a tank; a supply conduit and a pump for pumping fluid from said tank into said supply conduit; a preselector valve having a first port connected to said supply conduit, a second port connected to said tank, a third port and a fourth port connected to said second work conduit of said double-acting consumer, said preselector valve having a first position in which fluid communication is established in said preselector valve between said first and fourth ports and also between said second and third ports and having a second position in which fluid communication is established in said preselector valve between said first and third ports and also between said second and fourth ports; a control valve having a first port connected to said first work conduit of said double-acting consumer and having a second port connected to said third port of said selector valve and having a first position in which fluid communication between said ports of said control valve in said control valve is blocked and having a second position in which fluid communication between said ports of said control valve in said control valve is established; and pressureregulating means connected between said fourth port of said preselector valve and said tank and operative for regulating the fluid pressure in said second work conduit.

2. The apparatus defined in claim 1, and further including an additional consumer having a respective first work conduit for receipt of pressure fluid to cause said second consumer to effect movement of a load in a first direction, and further including an additional control valve having a respective first port connected to said first work conduit of said additional consumer and having a respective second port connected to said third port of said preselector valve and having a respective first position in which fluid communication between said ports of said additional control valve in said additional control valve is blocked and having a respective second position in which fluid communication between said ports of said additional control valve in said additional control valve is established.

3. The apparatus defined in claim 2, said additional consumer further having a respective second work conduit for receipt of pressure fluid to cause said additional consumer to effect movement of its load in a second direction opposite the respective first direction, said second work conduit of said additional consumer being connected to said fourth port of said preselector valve.

4. The apparatus defined in claim 1, and further including a check valve connected between said first and second ports of said preselector valve with an orientation allowing the flow of fluid through said check valve from said second port of said preselector valve to said first port of said preselector valve, whereby the flow of fluid into said first work conduit will cause a sucking of fluid into said second work conduit of said consumer device via said check valve.

5. The apparatus defined in claim 1, wherein said pressure-regulating means comprises a flow restrictor connected between said fourth port of said preselector valve and said tank and operative for diverting back to said tank part of the fluid flowing out of said fourth port of said preselector valve and into said second work conduit, whereby to maintain the fluid pressure in said second work conduit at a less than maximum value.

6. The apparatus defined in claim 5, wherein said flow restrictor is adjustable.

7. The apparatus defined in claim 1, wherein said pressure-regulating means comprises a pressurelimiting valve having one port connected to said fourth port of said preselector valve and another port connected to said tank and operative for limiting the pressure of fluid flowing out of said fourth port of said preselector valve into said second work conduit of said consumer.

8. The apparatus defined in claim 1, wherein said control valve is of the seated-valve-member type and is comprised of at least one valve member movable between first and second positions to respectively cause said control valve to assume said first and second positions thereof, spring biasing means for normally urging said at least one valve member to the first position thereof, and actuating means for opposing the force of said spring biasing means to bring said at least one valve member to the second position thereof.

9. The apparatus defined in claim 1, wherein said preselector valve is comprised of at least one valve member movable between first and second positions to respectively cause said preselector valve to assume said first and second positions thereof, spring biasing means for normally urging said at least one valve member to the first position thereof and single-acting electromagnet means operative for opposing the force of said spring biasing means and moving said at least one valve member to the second position thereof.

10. The apparatus defined in claim 1, wherein said preselector valve has an intermediate third position in which fluid communication is established in said preselector valve among said second, third and fourth ports thereof and in which said first port thereof is blocked.

ll. The apparatus defined in claim 1, wherein said preselector valve has an intermediate third position in which fluid flow through said first, second, third and fourth ports thereof is. blocked.

12. The apparatus defined in claim 1, further including a check valve connected between said supply conduit and said first port of said preselector valve with such a direction as to permit flow through said check valve into said first port of said preselector valve.

13. The apparatus defined in claim 1; and further comprising additional pressure-regulating means operative for regulating the pressure of fluid in said first work conduit of said consumer.

14. The apparatus defined in claim 1; and further comprising additional pressure-regulating means connected between said first port of said preselector valve and said tank and operative for regulating the pressure of fluid entering said first port of said preselector valve.

15. The appratus defined in claim 13, wherein said additional pressure-regulating means comprises a pressure-limiting valve connected between said supply conduit and said tank.

16. The apparatus defined in claim 2, wherein the two consumers are the moving means of a hydraulic-lift tail gate arrangement mounted for swinging movement under the control of the first consumer and for vertical movement under the control of the additional consumer.

17. The apparatus defined in claim 1, wherein said pressure-regulating means comprises means operative for maintaining the fluid pressure in said second work conduit at a first value; and further including additional pressure-regulating means operative for maintaining the fluid pressure in said first work conduit at a higher second value.

18. The apparatus defined in claim 1, wherein said pressure-regulating means comprises pressure-limiting means connected between said fourth port of said preselector valve and said tank and operative for limiting the pressure of fluid in said second work conduit to a first constant value, and further including pressurelimiting means connected between said supply conduit and said tank and operative for limiting the pressure of fluid in said supply conduit to a higher second constant value. 

1. A hydraulic control apparatus comprising, in combination, a double-acting consumer having a first work conduit for receipt of pressure fluid to cause said consumer to effect movement of a load in a first direction and having a second work conduit for receipt of pressure fluid to cause said consumer to effect movement of such load in opposite second direction; a tank; a supply conduit and a pump for pumping fluid from said tank into said supply conduit; a preselector valve having a first port connected to said supply conduit, a second port connected to said tank, a third port and a fourth port connected to said second work conduit of said double-acting consumer, said preselector valve having a first position in which fluid communication is established in said preselector valve between said first and fourth ports and also between said second and third ports and having a second position in which fluid communication is established in said preselector valve between said first and third ports and also between said second and fourth ports; a control valve having a first port connected to said first work conduit of said double-acting consumer and having a second port connected to said third port of said selector valve and having a first position in which fluid communication between said ports of said control valve in said control valve is blocked and having a second position in which fluid communication between said ports of said control valve in said control valve is established; and pressure-regulating means connected between said fourth port of said preselector valve and said tank and operative for regulating the fluid pressure in said second work conduit.
 2. The apparatus defined in claim 1, and further including an additional consumer having a respective first work conduit for receipt of pressure fluid to cause said second consumer to efFect movement of a load in a first direction, and further including an additional control valve having a respective first port connected to said first work conduit of said additional consumer and having a respective second port connected to said third port of said preselector valve and having a respective first position in which fluid communication between said ports of said additional control valve in said additional control valve is blocked and having a respective second position in which fluid communication between said ports of said additional control valve in said additional control valve is established.
 3. The apparatus defined in claim 2, said additional consumer further having a respective second work conduit for receipt of pressure fluid to cause said additional consumer to effect movement of its load in a second direction opposite the respective first direction, said second work conduit of said additional consumer being connected to said fourth port of said preselector valve.
 4. The apparatus defined in claim 1, and further including a check valve connected between said first and second ports of said preselector valve with an orientation allowing the flow of fluid through said check valve from said second port of said preselector valve to said first port of said preselector valve, whereby the flow of fluid into said first work conduit will cause a sucking of fluid into said second work conduit of said consumer device via said check valve.
 5. The apparatus defined in claim 1, wherein said pressure-regulating means comprises a flow restrictor connected between said fourth port of said preselector valve and said tank and operative for diverting back to said tank part of the fluid flowing out of said fourth port of said preselector valve and into said second work conduit, whereby to maintain the fluid pressure in said second work conduit at a less than maximum value.
 6. The apparatus defined in claim 5, wherein said flow restrictor is adjustable.
 7. The apparatus defined in claim 1, wherein said pressure-regulating means comprises a pressure-limiting valve having one port connected to said fourth port of said preselector valve and another port connected to said tank and operative for limiting the pressure of fluid flowing out of said fourth port of said preselector valve into said second work conduit of said consumer.
 8. The apparatus defined in claim 1, wherein said control valve is of the seated-valve-member type and is comprised of at least one valve member movable between first and second positions to respectively cause said control valve to assume said first and second positions thereof, spring biasing means for normally urging said at least one valve member to the first position thereof, and actuating means for opposing the force of said spring biasing means to bring said at least one valve member to the second position thereof.
 9. The apparatus defined in claim 1, wherein said preselector valve is comprised of at least one valve member movable between first and second positions to respectively cause said preselector valve to assume said first and second positions thereof, spring biasing means for normally urging said at least one valve member to the first position thereof and single-acting electromagnet means operative for opposing the force of said spring biasing means and moving said at least one valve member to the second position thereof.
 10. The apparatus defined in claim 1, wherein said preselector valve has an intermediate third position in which fluid communication is established in said preselector valve among said second, third and fourth ports thereof and in which said first port thereof is blocked.
 11. The apparatus defined in claim 1, wherein said preselector valve has an intermediate third position in which fluid flow through said first, second, third and fourth ports thereof is blocked.
 12. The apparatus defined in claim 1, further including a check valve connected between said supply conduit and said fiRst port of said preselector valve with such a direction as to permit flow through said check valve into said first port of said preselector valve.
 13. The apparatus defined in claim 1; and further comprising additional pressure-regulating means operative for regulating the pressure of fluid in said first work conduit of said consumer.
 14. The apparatus defined in claim 1; and further comprising additional pressure-regulating means connected between said first port of said preselector valve and said tank and operative for regulating the pressure of fluid entering said first port of said preselector valve.
 15. The appratus defined in claim 13, wherein said additional pressure-regulating means comprises a pressure-limiting valve connected between said supply conduit and said tank.
 16. The apparatus defined in claim 2, wherein the two consumers are the moving means of a hydraulic-lift tail gate arrangement mounted for swinging movement under the control of the first consumer and for vertical movement under the control of the additional consumer.
 17. The apparatus defined in claim 1, wherein said pressure-regulating means comprises means operative for maintaining the fluid pressure in said second work conduit at a first value; and further including additional pressure-regulating means operative for maintaining the fluid pressure in said first work conduit at a higher second value.
 18. The apparatus defined in claim 1, wherein said pressure-regulating means comprises pressure-limiting means connected between said fourth port of said preselector valve and said tank and operative for limiting the pressure of fluid in said second work conduit to a first constant value, and further including pressure-limiting means connected between said supply conduit and said tank and operative for limiting the pressure of fluid in said supply conduit to a higher second constant value. 